Cyanine dye containing a tetrahydrobenzothiazole nucleus



Patented Dec. 14, 1943 UNH'ED STATES ans,

CYAN NE DYE CONTAINING A TETR-AHY- DROBENZOTHIAZOLE NUCLEUS Leslie G. S.Brooker and Frank L. White, Rochester, N. Y., assignors to Eastman KodakCompany, Rochester, N. Y., a corporation of New Jersey 7 Claims.

This invention relates to cyanine dyes containing atetrahydrobenzothiazole nucleus and to a process for preparing the same.This application is a division of our copending application Serial No.303,618, filed November 9, 1939.

Cyanine dyes contain at least two auxochromic nitrogen atoms, the oneternary and the other quaternary, the one nitrogen atom lying in oneheterocyclic nucleus and the other lying in another heterocyclicnucleus, the two nitrogen atoms being connected by a conjugated carbonchain. A number of cyanine dyes containing benzothiazole nuclei as oneor both of the aforesaid heterocyclic nuclei are known.

We have now found that it is possible to prepare certain unsymmetricalcarbocyanine dyes in which one of the aforesaid auxochromic nitrogenatoms lies in a 4,5,6,7-tetrahydrobenzothiazole nucleus and the otherauxochromic nitrogen atom lies in a benzothiazole or benzoxazolenucleus. We have further found that these new cyanine dyes sensitizephotographic emulsions strongly and cleanly, i. e. without producingexcessive fog.

It is, accordingly, an object of our invention to provide newcarbocyanine dyes. A further object is to provide a method for preparingsuch dyes. A further object is to provide photographic emulsionssensitized with such dyes. Other objects will appear hereinafter.

As starting materials for the preparation of our new dyes, we employ2-methyl-4,5,6,7-tetrahydrobenzothiazole. We first convert this into aquaternary salt by reacting the base with an ester, such as an alkylhalide, an alkyl sulfate or an alkyl-p-toluenesulfonate, for example.

To prepare unsymmetrical carbocyanine dyes from the2-methyl-4-5,6,7-tetrahydrobenzothiazole quaternary salts, we react thequaternary salts with benzothiazole or benzoxazole quaternary saltscontaining a fi-arylaminovinyl roup in the alpha position, in thepresence of an acid binding agent, e. g. pyridine.

The following examples will serve to demonstrate the manner of obtainingour new dyes. These examples, however, are not intended to limit ourinvention.

EXAMPLE 1.3,3'-diethyl-4',5',6,7'-tetrahydro- 3.53 g. (1.1 mol.) of2methyl-4,5,6,7-tetrahydrobenzothiazole etho-p-toluenesulfonate and 3.95g. (1 mol.) of Z-(fi-acetanilidovinyl)-benzoxazole ethiodide were mixedtogether in 15 cc. of dry pyridine. gently boiled, under reflux, forabout 10 minutes. The reaction mixture was then cooled and dilute-clwith 150 cc. of diethyl ether. The ethereal layer was decanted and theresidue was stirred with 56 cc. of hot acetone. The resulting acetonesuspension was chilled to 0 C. and the dye was filtered on and washedwith cold acetone. The dye was allowed to dry in the air. The yield ofcrude dye was 45% and after two recrystallizations from methyl alcohol(45 cc. per gram of dye), a 26% yield of pure dye was obtained. The puredye was obtained in the form of dark purple crystalshaving a blue reflexand melting at 24=7 to 248 C. with decomposition.

hydrothiacarbocyanine iodide 4.42 g. (1.3 mol.) of2-methyl-4,5,6,7-tetrahydrobenzothiazole metho-p-toluenesulfonate and4.5 g. (1 mol.) of 2-(B-acetanilidovinyl)-benzo.- thiazole ethiodidewere mixed together in 15 cc. of dry pyridine. The resulting mixture wasgently boiled, under reflux, for about 10 minutes. The reaction mixturewas then chilled and the crystalline dye which separated was filteredoff, washed with acetone and allowed to dry in the air. The yield ofcrude dye was 62% and after recrystallization from methyl alcohol coppergram of dye), a yield of pure dye of 42% was obtained. The pure dye wasin the form of dark green needles having a blue reflex and melting at273 to 274 C. with decomposition.

2-methyl-4,5,6,7-tetrahydrobenzothiazole can be prepared as described bySmith and Sapiro in Transactions of the Royal Society of South Africa,vol. 18, pages 229-235 (1929) Quaternary salts of2-methyl-4,5,6,'7-tetrahydrobenzothiazole can be prepared as illustratedin the following examples.

The resulting mixture was EXAMPLE 3.-2-methyZ-4,5,6,7-tetrahydrobenzo#thiazole ethiodide 1.53 g. of 2-methyl-4,5,6,7-tetrahydrobenzothiazoleand 2.0 g. of ethyl iodide were heated together, under reflux, for about24 hours. The solid reaction product consists essentially of thequarternary salt and can be used without further purification.

EXAMPLE 4.-2-m thyl-4,5,6,7-tetrahydrobenzothiazoleetho-p-toluenesulfonate V 3.06 g. of 2-methyl-4,5,6,7-tetrahydrobenz0thiazole and 4.0 g. of ethyl-p-toluenesulfonate wereheated together at 100 C. for four days. The solid reaction productconsists essentially of the quaternary salt and can be used withoutfurther purification. The metho-p-toluenesulfonate can be similarlyformed by using methyl instead of secure best results. V

The concentration of our new dyes in the emulsions can vary widely, e.g. from about 5 to about 100 mg. per liter of flowable emulsion. Theconcentration of the dye will vary according to the type oflight-sensitive material in the emulsion and-according to the effectsdesired. The suitable and most economical concentration for any givenemulsion will be apparent to those skilled in the art, upon making theordinary tests and observations customarily used in the art ofemulsion-making. To prepare a gelatino-silverhalide emulsion sensitizedwith one of our new dyes, the following procedure is satisfactory: aquantity of the dye-is dissolved in methyl alcohol, and a volume of thesolution (which may be diluted with water) containing from 5 to 100 mg.of dye is slowly added to about 1000 cc. of a gelatino-silverehalideemulsion with stirring. Stirring is continued until the dye is uniformlydispersed. With the more powerful of our new sensitizing dyes, 10 to mg.of dye per 1000 ccjof emulsion suifice to produce the maximumsensitizing effect with the ordinary gelatino-silverhalide emulsions.The above statements are only illustrative and not to be understood aslimiting our invention in any sense, as it will be apparent that ourdyes can be incorporated by other methods in many of the photographicemulsions customarily employed in the art, such, for instance, as bybathing the plate or film upon which the emulsion is coated, in asolution of the dye in an appropriate solvent, although such a method isordinarily not to be preferred. The claims are intended to cover anycombination of these new dyes with a photographic silver halide emulsionwhereby the dyes exert a sensitizing effect on the emulsion.

The following table contains data which show the sensitizing range ofour new dyes on photographic silver halide emulsions:

the finished, washed emulsions and should be uniformlydistributedthroughout to Photographic 7 elements comprising our new dyescan be prepared in the usual manner by coating the emulsions on asuitable support (e. g. glass; cellulose derivative film, resin film orphotographic paper) to suitable thickness and drying the coatedemulsion.

It is well known that cyanine dyes resonate between two extreme formsand that a cyanine dye can be represented by either of the two extremeforms. Thus, the instant dyes can be represented by either of thefollowing general formulas:

What we claim as our invention anddesire to be secured by Letters Patentof the United States is: T

1. A' dye'selected from the group characterized by the following generalformula;

wherein Q represents a member selected from the group consisting ofoxygen and sulfur atoms, R and R represent alkyl groups and X representsan acid radical.

2. A dye selected from the group characterized by the following generalformula:

3. A dye selected from the group characterized 4.3-ethyl-3-methy1-4',5',6',7-tetrahydrothiaby the following generalformula: carbocyanine iodide.

H9 5. 3,3'-diethyl-4',5',6',7'-tetrahydro oxathia- C S 0 carbocyanineiodide. 1120/ s. A 3-ethyl-3'-methyl-4,5',6,7'-tetrahydr0- H (i) :5C=OE-CH=CHC thiacarbocyanine salt.

2 7. A3,3-diethyl-4,5,6',7'-tetrahydro-oxathia- N N carbocyanine salt.

2 LESLIE G. s. BROOKER.

wherein R and R represent alkyl groups and X 10 FRANK WHITE representsan acid radical.

